This application is based on patent application No. 10-257192 filed in Japan, the contents of which are hereby incorporated by references.
This invention relates to an image processor, an image combining method, an image pickup apparatus provided with an image processor, and a computer-readable storage medium storing an image combination program.
Conventionally, in the field of a digital video camera, a digital still camera and like image pickup apparatus using a solid-state image sensor such as a Charge Coupled Device (CCD), there have been known methods for improving a resolution according to which an object image is partially picked up using a plurality of image sensors, and a whole object image is produced by combining partial images in an image processing as disclosed in, for example, Japanese Unexamined Patent Publications No. 5-137059 and No. 6-141246.
Further, U.S. Pat. No. 4,734,782 discloses an image processor in which an image of an original divided into two pieces with an overlapping boundary portion is picked up by two image sensors, and picked images are combined together at the boundary portions to form a whole image, and intermediate tones can be reproduced by area gradation. In this apparatus, a parameter of the area gradation at a joint portion of the two images is made continuous in order to realize a continuous area gradation at the joint portion.
As a technique for uniforming a density difference between a plurality of images continuously picked up and uniforming a density difference among a plurality of images when they are formed on the same sheet, Japanese Unexamined Patent Publication No. 2-288667 discloses a digital image density uniforming method in which an average density of an arbitrary area of an image as a reference and a density of a corresponding area of another image to be subjected to density conversion are calculated, and the density of the image to be subjected to density conversion is corrected based on a difference between the calculated densities.
In the case that a whole object image is obtained by dividing an object into several sections, picking up images of these sections by a plurality of color image sensors, and pasting picked partial images together, a color discontinuity occurs at a joint portion due to a color displacement unless a white balance (WB) adjustment is applied the respective partial images in a matching manner. As a result, the obtained picked image undesirably has an unnatural color tone.
The above-mentioned Japanese Unexamined Patent Publication Nos. 5-137059 and 6-141246 disclose a technique for dividing a whole object into sections and picking up images of these sections by a plurality of image sensors. However, these publications disclose neither the problem of the color discontinuity at the boundary portions of the picked images resulting from the variant WB adjustment applied to the partial images, nor a method for solving this problem.
Further, the image processor disclosed in the above-mentioned U.S. Pat. No. 4,734,782 is designed to prevent an occurrence of a density discontinuity at the joint portion of two monochromatic picked images, but not to prevent an occurrence of a color discontinuity caused by the color displacement of the color images. Neither does this publication disclose a method for solving this problem.
The method disclosed in the above-mentioned Japanese Unexamined Patent Publication No. 2-288667 is designed to correct a density difference between a plurality of monochromatic images. However, this publication neither mentions the aforementioned problem of the color discontinuity in the color image, nor indicates a means for solving this problem.
It is an object of the invention to provide an image combination technique which has overcome the problems residing in the prior art.
It is another object of the invention to provide an image processor and image combining method which can produce a picked image by combining a plurality of partial images having inconspicuous color discontinuities.
According to an aspect of the invention, a plurality of images are combined. A first correction amount for pixel data of a first color image having a plurality of color components and a second correction amount for pixel data of a second color image having the same color components are calculated in the aspect of at least one of the plurality of color components based on pixel data of at least a boundary portion of each of the first and second color images in the aspect of the at least one color component. The pixel data of the first color image and the pixel data of the second color image are corrected based on the first and second correction amounts respectively to reduce a color tone difference between the first and second color images. The corrected first and second color images are combined with each other at their respective boundary portions.
The first and second correction amounts may be calculated by calculating an average value of pixel data of at least a boundary portion of the first color image and an average value of pixel data of at least a boundary portion of the second color image in the aspect of at least one of the plurality of color components, and calculating a first offset amount for the pixel data of the first color image and a second offset amount for the pixel data of the second color image based on calculated average values in the aspect of the at least one color component. In this case, the first and second color image may be corrected by adding the first offset amount to the pixel data of the first color image and the second offset amount to the pixel data of the second color image to correct the color tone of the first and second color images.
These and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments when the same is read in conjunction with the accompanying drawings.